1. Field of the Invention
The present invention relates to communications based on a modulation scheme, such as a phase-based modulation scheme like quadrature-phase, shift-keying (QPSK) modulation.
2. Description of the Related Art
In a typical fiber-to-the-curb (FTTC) telecommunication system, signals are transmitted between a central office (CO) and one or more remote nodes as optical signals over optical fibers, while signals are transmitted between each remote node and one or more consumer product equipment (CPE) units (e.g., telephones, faxes, computers) as electrical signals over copper wires. As such, each remote node has components for receiving downstream optical signals from the CO, converting the optical signals into electrical signals, and transmitting the electrical signals to the CPE units. Similarly, each remote node has components for receiving upstream electrical signals from the CPE units, converting the electrical signals into optical signals, and transmitting the optical signals to the CO.
In one possible implementation of an FTTC telecommunication system, at least some of the signals received by the remote nodes are signals that have been modulated using a phase-based modulation scheme, such as quadrature-phase, shift-keying (QPSK) modulation. For example, either or both of the downstream optical signals and/or the upstream electrical signals received by the remote nodes may be QPSK signals. In such an implementation, each remote node has one or more QPSK receivers for receiving the QPSK signals for subsequent conversion (i.e., from optical to electrical or from electrical to optical) and further transmission. In general, it is desirable to implement QPSK receivers that require relatively low amounts of power for use in the remote nodes of an FTTC telecommunication system where the power available at each remote node may be limited.
The present invention is directed to a scheme for efficiently using power in a receiver designed for QPSK or other modulated signals. According to one embodiment, the present invention is a receiver for an input signal generated using a modulation scheme, wherein the receiver is adapted to generate a variance of a constellation corresponding to the input signal and to adaptively adjust its processing based on the variance, for example, to reduce power consumption or error rate in the receiver.